Climate data continuity with ASOS rain observations

The National Weather Service has placed the Automated Surface Observing System (ASOS) in service during the 1990s. An improved Heating Tipping Bucket (HTB) rain gage was introduced beginning in May 1996 and continuing until all sites had the modifications. A comparison of thirteen locations using one-minute ASOS observations was reported earlier for concurrent observations for precipitation. A more complete set of locations (37) have now been used to compare operational Summary of the Day observations for precipitation to show the relationship of the ASOS HTB and the Universal Rain Gage. Results of the comparisons will be shown along with details of the effect the ASOS has had on the continuity of precipitation data.

ASOS temperatures have been shown in previous results to be mostly cooler than the predecessor instrument for approximately 90 locations. The next important question for many applications is how to estimate a climate normal or useful climate average. An approach will be discussed involving the comparison of ASOS to National Weather Service Cooperative sites within 50 km. Results will be presented showing that these comparisons can be useful but also complicated. An example will be given for St. Louis, MO where the utilities have a strong concern related to operations and rate adjustments.